Ok, now I start to understand. The current implementation only supports PPPoE with automatic assingment of IP address and DNS. Furthermore, take into account that 1.3.X is development version, it may have bugs. Anyway maybe we can implement what you are asking for in the future, but I can't give you any dates.
I agree that in your case with eBox 1.2 that doesn't support PPPoE method on the interfaces is better for you as it doesn't hides the ppp interfaces. We'll see what we finally do about it in 1.3.